This invention relates to a tamper-evident lid for a container having a lid which is removed by rotating it. This is an improvement upon the tamper-evident lid contained in the inventor's U.S. Application Ser. No. 549,975, filed Nov. 9, 1983.
In the prior application, there is disclosure of a tamper-evident lid comprising a disc which covers the open neck of a container, and the disc carries an indicator on its top. The indicator is, for example, in the form of microcapsules of a color-changeable dye or ink supported on a paper layer and the ink is a conventional leuco dye. Such dye is available from Appleton Papers, Inc. of Appleton, Wisconsin. Also, NCR Paper SC White 190, also made by Appleton Papers, Inc., is a paper coated with such a leuco dye. The indicator in its microcapsules is activated by rubbing it. In the lid of the container, there are means for rubbing the indicator for activating it upon rotation of the lid on the container. A person can ascertain from the presence or absence of a visible indication at the indicator on the disc whether the lid had been rotated, i.e. whether an effort had been made to remove the container lid.
Rubbing the indicator requires adequate and sufficiently distributed pressure between the rubbing means in the lid and the indicator supported on the disc at the neck of the container. Where the indicator comprises a sheet of microcapsules filled with an ink or leuco dye, which becomes visible upon exposure to air, it is necessary that a large quantity of capsules near each other be broken before the indication will become dark enough. Therefore, the rubbing means must rupture sufficient microcapsules.
The disc at the top of the container may yield and deflect under the pressure exerted by the lid and it may bow downwardly at its center. The rubbing means in the lid may not uniformly rub the indicator so that the entire indicator layer of capsules may not be uniformly activated. Also, due to manufacturing tolerances in the container, disc and/or lid, the rubbing means in the lid may be tilted slightly with respect to the indicator layer on the disc so that there is not uniform activation of the indicator across the whole indicator layer.
The conventional disc installed at the neck of the container for sealing closed the opening in the neck is usually a piece of paper, perhaps wax coated, a piece of plastic, metal foil, etc. In the invention of U.S. Application Ser. No. 549,975, a thin, multi-layer disc is used. It has a base or substrate of a thin, somewhat rigid layer, e.g. of polyethylene plastic, for support of the layers above it for ensuring secure engagement between the indicator and the rubbing means. A thin layer of resilient material, e.g. foam material, is disposed over the substrate. The resilient foam material biases the next described indicator layer toward the rubbing means. Above the foam material is the indicator, contained in a thin layer of microcapsules disposed on a paper substrate, for example. The microcapsules contain a dye or ink which darkens when exposed to air, which exposure occurs through rupturing of the capsules. The height of the multi-layer disc is selected to cooperate with the height of the rubbing means at the lid so that the indicator and the rubbing means firmly engage. Beneath the base or substrate is a ring of adhesive by which the disc is non-rotatably adhered to the neck of the container. But, the adhesive permits the disc to be removed from the container once the lid of the container has been removed. Means may be provided for rigidifying the disc for further ensuring secure engagement between the indicator layer and the rubbing means in the lid.
The lid of the container is of the type which is rotated for removal. It may be a screw type. Alternatively, it may be the type with a flange which engages beneath a collar on the container neck and the lid flange includes a radially inwardly projecting tab or key which locks beneath the collar of the container until the lid has been rotated to a position where the key on the lid is aligned with a keyway in the collar of the bottle. Upon this alignment, the lid may be lifted free of the container.
Rubbing means are carried at the underside of the lid. The lid is shaped so that the rubbing means cooperate with the indicator at the top of the disc to rub the indicator and break the microcapsules. The rubbing means are preferably in the form of an abrasive material which is either molded directly into the underside of the lid, e.g. when the lid is molded, or is provided on the underside of a second disc which is supported beneath the top of the lid. Where a disc is provided under the lid, the abrasive may be supported on a resilient layer, such as a foam backing, which would also bias the abrasive down toward the indicator beneath it, for assuring secure engagement between them.
The user must be able to view the indicator to see whether it has been activated. The lid may be of light transmitting, transparent or translucent material, so that the indicator may be visible through the lid. The visibility problem is resolved by providing an interruption in the abrasive material, through which a clear view of the indicator beneath is made possible.